(a) Field of the Invention
The present invention relates to the sterilization or other treatment of materials by application of a very high pressure.
(b) Background Art
The effects of high pressure (up to 120,000 PSI) on food micro organisms was first studied as early as 1899 on milk, meats, fruits and vegetables. Early researchers demonstrated some astonishing results. After storage at room temperature, peach and pear samples preserved by brief exposure to high pressures had not deteriorated after five years. Meat that was packaged after such sterilization showed no signs of microbial deterioration when opened after three months of storage. The shelf life of milk was extended by one day. Many foods appear to be particularly favorable to ultra high pressure food preservation, such as acidic foods that naturally inhibit surviving spore nucleation. Examples of recent work indicated that freshly squeezed orange juice treated by this high pressure process showed no signs of contamination after seventeen months of storage. A search of the patent literature discloses a number of methods of pressurizing various products as a means of sterilization. These are the following:
U.S. Pat. No. 1,355,476 (Hering) discloses an apparatus for destruction of cellular structures, such as bacteria or other small living organisms, by means of rapid successive positive and negative pressure changes in a confined liquid. In one arrangement there is a plunger and cylinder to create the pressure. In another arrangement there is a hammer which is permitted to drop onto a plunger "P" which causes an abrupt increase in pressure, after which the hammer is raised to release the pressure.
U.S. Pat. No. 1,711,097 (Kratzer) shows a system for sterilizing substances. This is accomplished by subjecting the substance to be sterilized to a pressure considerably in excess of atmospheric pressure and permitting it to remain at that pressure for a time sufficient to cause the excess pressure gases to permeate the cell envelope. The cell is then suddenly subjected to a very much reduced pressure, and it is alleged that the result is that the contained gases of the cell envelope suddenly expand, rupturing the same and killing the cell.
U.S. Pat. No. 1,728,334 (Crowther) shows a system for sterilizing where the material is placed in a tube 42. Then a gaseous medium under pressure is directed through an inner tube 44 to pressurize the area within the tube 42 and cause sterilization of the contained material.
U.S. Pat. No. 2,069,820 (Dodge) shows a sterilizing apparatus where there is a plunger 6 that is moved inwardly on a compression stroke and outwardly on the return stroke by a crank 7. At the opposite end of the cylinder there is an auxiliary plunger 10 that is held in place by a spring 11. Fluid to be sterilized is directed into a compression chamber 5 through an inlet 14 positioned adjacent to the plunger 6 in its retracted position. An outlet port 15 is positioned at the opposite end of the chamber 5. The cycle is shown in FIG. 3, and during the period "A", fluid is directed through the inlet 14 into the chamber 5. The previously sterilized fluid in the chamber 5 is pushed through the outlet 15, but the fluid taken in does not move totally to the outlet 15, so that it does not mix with the sterilized fluid that has been discharged. During portion "B" of the cycle, the plunger 6 is moved inwardly to compress the fluid, and during the cycle portion "C" the plunger 6 is retracted. In the final interval "D" of the cycle the plunger 6 is drawn further out creating subatmospheric pressure in the fluid, and following this interval the valves 17 and 16 for the inlet and outlet 15 and 17, respectively, are opened to place an additional charge of fluid into chamber 5 and cause the sterilized fluid to flow out the port 15. The auxiliary plunger 10 is pushed outwardly to some extent against the spring 11 during the compression stroke, and then the spring 11 pushes the plunger 10 inwardly on the return stroke of the plunger 6. It is also stated that the fluid is compressed to some extent, and the energy released in the expansion of the fluid in the chamber 5 subsequent to compression is returned back to the plunger 6 and to the flywheel. It is further stated that three or more compressors may be used so that there can be practically a continuous flow of fluid which is being treated, and that repeated compression strokes could be used on the fluid.
U.S. Pat. No. 4,030,406 (Wander et al) discloses an apparatus for sterilization by internal heating effects and centrifugal force. The heating is accomplished by friction arising between the product and the moving surface and subjecting the material to centrifugal force causes an increase in pressure.
To the best knowledge of the applicants herein, the sterilization of liquid, semi-liquid and solid materials, such as food products or other products requiring sterilization, by utilizing very high pressure, has not experienced any substantial commercial application. Accordingly, it is the object of the present invention to provide an apparatus and method which has certain desirable characteristics which enhance the capability of properly accomplishing the sterilization in a commercially feasible manner.